Fusion:
Basic Principles, Current Progress and ITER Plans
Mohamed Abdou
Distinguished Professor, Mechanical and Aerospace Engineering Department
Director, Center for Energy Science and Technology Advanced Research (CESTAR)
Director, Fusion Science and Technology Center
University of California Los Angeles (UCLA)
Plenary Talk presented at the 9th International Cairo Conference on Energy and Environment
What is Nuclear Fusion?
•
•
Nuclear Fusion is the energy-producing process taking place in the core of
the Sun and stars
The core temperature of the Sun is about 15 million °C. At these
temperatures hydrogen nuclei fuse to give Helium and Energy. The
energy sustains life on Earth via sunlight
Energy Released by
Nuclear Reactions
• Light nuclei (hydrogen, helium) release
energy when they fuse (Nuclear Fusion)
• The product nuclei weigh less than the
parent nuclei
• Heavy nuclei (Uranium) release energy
when they split (Nuclear Fission)
• The product nuclei weigh less than the
original nucleus
Energy Released by Nuclear
Fusion and Fission
• Fusion reactions release much higher energies
than Fission reactions
Fusion Reactions
• Deuterium – from water
(0.02% of all hydrogen is heavy hydrogen or
deuterium)
• Tritium – from lithium
(a light metal common in the Earth’s crust)
Deuterium + Lithium → Helium + Energy
This fusion cycle (which has the fastest
reaction rate) is of interest for Energy
Production
The World, particularly developing countries, needs a New
Energy Source
• Growth in world population and growth in energy demand from
increased industrialisation/affluence will lead to an Energy Gap which will
be increasingly difficult to fill with fossil fuels
• Without improvements in efficiency we will need 80% more energy by 2020
• Even with efficiency improvements at the limit of technology we would still
need 40% more energy
Incentives for Developing Fusion
• Fusion powers the Sun and the stars
– It is now within reach for use on Earth
• In the fusion process lighter elements are “fused”
together, making heavier elements and producing
prodigious amounts of energy
• Fusion offers very attractive features:
– Sustainable energy source
(for DT cycle; provided that Breeding Blankets are successfully
developed)
– No emission of Greenhouse or other polluting gases
– No risk of a severe accident
– No long-lived radioactive waste
• Fusion energy can be used to produce electricity
and hydrogen, and for desalination
Fission (PWR)
Fusion structure
Coal
Tritium in fusion
Fusion Energy – Disadvantages
• Fusion reaction is difficult to start!
– High temperatures (Millions of degrees) in a
pure High Vacuum environment are required
– Technically complex and high capital cost
reactors are necessary
• More Research and Development is
needed to bring concept to fruition
– The physics is well advanced but requires
sustained development on a long time scale
(20 to 40 years)
The President recognizes Fusion’s potential
Fusion
Fusion Power Station Schematic
Plasmas
• A Plasma is an ionised gas. A mixture of positive ions
and negative electrons with overall charge neutrality
• Plasmas constitute the 4th state of matter, obtained at
temperatures in excess of 100,000 degrees
• Plasmas conduct electricity and heat
Self-Sustaining or ‘Ignited’ Plasmas
• Deuterium – tritium fusion reaction:
D + T → 4He + n + Energy
The 4He nuclei (‘a’ particles) carry about 20% of the energy and
stay in the plasma. The other 80% is carried away by the neutrons
and can be used to generate steam.
Plasmas become Self-sustaining or Ignited when there is enough
a power to balance losses from the plasma
• In stars plasma particles (including a’s) are confined mainly by
gravity and high plasma densities achieved
• On Earth:
– hot dense plasmas can be confined in Magnetic fields (Magnetic
Confinement Fusion)
– superdense plasmas can be obtained by imploding solid deuteriumtritium pellets (Inertial Confinement Fusion)
Inertial Confinement
• Laser implosion of small (3mm diameter) solid deuterium–tritium
pellets produces fusion conditions
• Pressure generation
• Compression
Fuel is compressed by rocket-like blow off
200,000 million atmospheres in core
• Ignition and burn
– Peak compression fuel reaches 1000-10000 times liquid density for
extremely short time (10–11 seconds)
– Core is heated and ‘spark ignition’ occurs
Magnetic Confinement
• Magnetic fields cause charged particles to spiral
around field lines. Plasma particles are lost to the
vessel walls only by relatively slow diffusion across
the field lines
• Toroidal (ring shaped) system avoids plasma
hitting the end of the container
• The most successful Magnetic Confinement device
is the TOKAMAK (Russian for ‘Toroidal Magnetic
Chamber’)
The Tokamak:
A Transformer Device
How Large a Device?
• For fusion power to ignite a plasma:
– There has to be sufficient density of deuterium and tritium ions
(ni);
– The reacting ions have to be hot enough (Ti);
– The energy from the fusion a’s must be confined for long
enough (tE).
tE increases with the square of the device size
– a large machine is needed.
• The fusion triple product (niTitE) and the ion
temperature (Ti) must both be large enough (below a
certain temperature the fusion reaction probability is too
small)
pressure (niTi) ≥ 2 atmospheres
confinement time > 5 seconds
plasma ion temperature ≈ 100-200 Million °C
JET
(Joint European Torus)
• The Joint European Torus (“JET”) is the largest
magnetic fusion test device in the world.
• Situated at Culham, Oxfordshire, JET:
– was constructed between 1978-1983;
– has operated 1983 - present;
– is the largest Project in the European Union’s
Fusion programme
• The participating countries are the 15 EU
nations + Switzerland
• The Project has a capital investment of over
£500 Million and an Annual Budget of around
£53 Million
JET
• JET is a Tokamak with:
– Torus radius 3.1m
– Vacuum vessel 3.96m
high x 2.4m wide
– Plasma volume 80m3
– Plasma current up to
5MA
– Main confining field up
to 4 Tesla (recently
upgraded from 3.4
Tesla)
Progress with Magnetic
Confinement Fusion
• JET and the similar large Tokamaks in:
– USA
Tokamak Fusion Test Reactor (TFTR)
Doublet IIID Tokamak (DIIID)
– Japan Japanese Tokamak – 60U (JT-60U)
Have made significant progress in:
–
–
–
–
–
Technology of fusion;
Approaching the conditions of an Ignited plasma;
Predicting the behaviour of a reactor plasma;
Controlling impurities which enter the plasma
Operating with Tritium fuel
Progress towards Ignition
• The Fusion Triple Product
(PitE = niTitE) required to
reach ignition can be
compared with leading
edge performance of the
devices year-on-year.
• The best plasmas now
need an improvement of
only 6 in performance.
This requires a new larger
device.
Controlling Impurities
• Fuel Impurities are a major threat to reactor success
• Two primary sources of impurities exist:
– Helium “ash” from the fusion reaction
– Material impurities from plasma-wall interactions
• Impurities must be controlled since they:
– Radiate energy, and reduce the plasma temperature
– Dilute the fuel, thereby preventing ignition
• The “Magnetic Divertor” is a device for controlling
impurities. This has been tested successfully in JET.
Three different concepts have been compared.
Results agree with code predictions.
Progress with Magnetic
Confinement Fusion
Pumped Divertor in JET
• Impurities (C, Be) are produced by ion impact on target
and are ionised in the plasma and returned to target
Fusion Power Development
The diagram encompasses :
• Two pulses with 10% T in D in JET in 1991;
• A result from the D-T studies on TFTR (1993 to 1997);
• High fusion power and quasi-steady-state fusion power from the
>200 pulses with >40% T in D in the JET D-T experiments of 1997.
ITER Design - Main Features
Central
Solenoid
Outer Intercoil
Structure
Blanket
Module
Vacuum Vessel
Cryostat
Toroidal Field Coil
Port Plug (IC Heating
Poloidal Field Coil
Divertor
Machine Gravity Supports
Torus Cryopump
ITER Objectives
Programmatic
• Demonstrate the scientific and technological feasibility of fusion energy
for peaceful purposes.
Technical
• Demonstrate extended burn of DT plasmas, with steady state as the
ultimate goal.
• Integrate and test all essential fusion power reactor technologies and
components.
• Demonstrate safety and environmental acceptability of fusion.
ITER Parameters
Total fusion power
Q = fusion power/auxiliary heating power
Average neutron wall loading
Plasma inductive burn time
Plasma major radius
Plasma minor radius
Plasma current (inductive, Ip)
Vertical elongation @95% flux surface/separatrix
Triangularity @95% flux surface/separatrix
Safety factor @95% flux surface
Toroidal field @ 6.2 m radius
Plasma volume
Plasma surface
Installed auxiliary heating/current drive power
500 MW (700MW)
≥10 (inductive)
0.57 MW/m2 (0.8 MW/m2)
≥ 300 s
6.2 m
2.0 m
15 MA (17.4 MA)
1.70/1.85
0.33/0.49
3.0
5.3 T
837 m3
678 m2
73 MW (100 MW)
ITER Site Layout
ITER Location
Caradache (France)
Rokkasho (Japan)
Fusion Nuclear Technology (FNT)
Fusion Power & Fuel Cycle Technology
FNT Components from the edge of the
Plasma to TF Coils (Reactor “Core”)
1. Blanket Components
2. Plasma Interactive and High Heat Flux
Components
a. divertor, limiter
b. rf antennas, launchers, wave guides, etc.
3. Vacuum Vessel & Shield Components
Other Components affected by the
Nuclear Environment
4. Tritium Processing Systems
5. Instrumentation and Control Systems
6. Remote Maintenance Components
7. Heat Transport and Power Conversion
Systems
Shield
Blanket
Vacuum vessel
Radiation
Plasma
Neutrons
First Wall
Tritium breeding zone
Coolant for energy
conversion
Magnets
Blanket (including first wall)
Blanket Functions:
A. Power Extraction
–
Convert kinetic energy of neutrons and secondary gamma-rays into heat
–
Absorb plasma radiation on the first wall
–
Extract the heat (at high temperature, for energy conversion)
B. Tritium Breeding
–
Tritium breeding, extraction, and control
–
Must have lithium in some form for tritium breeding
C. Physical Boundary for the Plasma
–
Physical boundary surrounding the plasma, inside the vacuum vessel
–
Provide access for plasma heating, fueling
–
Must be compatible with plasma operation
–
Innovative blanket concepts can improve plasma stability and confinement
D. Radiation Shielding of the Vacuum Vessel
Blanket Materials
1.
Tritium Breeding Material (Lithium in some form)
Liquid: Li, LiPb (83Pb 17Li), lithium-containing molten salts
Solid: Li2O, Li4SiO4, Li2TiO3, Li2ZrO3
2.
Neutron Multiplier (for most blanket concepts)
Beryllium (Be, Be12Ti)
Lead (in LiPb)
3.
Coolant
– Li, LiPb
4.
– Molten Salt
– Helium
– Water
Structural Material
–
Ferritic Steel (accepted worldwide as the reference for DEMO)
–
Long-term: Vanadium alloy (compatible only with Li), and SiC/SiC
5.
MHD insulators (for concepts with self-cooled liquid metals)
6.
Thermal insulators (only in some concepts with dual coolants)
7.
Tritium Permeation Barriers (in some concepts)
8.
Neutron Attenuators and Reflectors
A Helium-Cooled Li-Ceramic Breeder Concept: Example
Material Functions
• Beryllium (pebble bed) for
neutron multiplication
• Ceramic breeder (Li4SiO4,
Li2TiO3, Li2O, etc.) for tritium
breeding
• Helium purge (low pressure)
to remove tritium through
the “interconnected
porosity” in ceramic breeder
• High pressure Helium
cooling in structure (ferritic
steel)
Several configurations exist (e.g. wall parallel or “head on”
breeder/Be arrangements)
Li/Vanadium Blanket Concept
Vanadium structure
Li
Lithium
Secondary Shield
Li
Primary Shield
Li
Reflector
Breeding Zone
(Li flow)
Primary shield
(Tenelon)
Secondary shield
(B4C)
Reflector
Vanadium structure
Lithium
Flows of electrically conducting
coolants will experience complicated
magnetohydrodynamic (MHD) effects
What is magnetohydrodynamics (MHD)?
– Motion of a conductor in a magnetic field produces an EMF that can
induce current in the liquid. This must be added to Ohm’s law:
j   (E  V  B )
– Any induced current in the liquid results in an additional body force
in the liquid that usually opposes the motion. This body force must
be included in the Navier-Stokes equation of motion:
V
1
1
 (V  )V   p   2 V  g  j  B
t


– For liquid metal coolant, this body force can have dramatic impact
on the flow: e.g. enormous MHD drag, highly distorted velocity
profiles, non-uniform flow distribution, modified or suppressed
turbulent fluctuations
Large MHD drag results in large
MHD pressure drop
Conducting walls
Insulated wall
Lines of current enter the low
resistance wall – leads to very
high induced current and high
pressure drop
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0.8
0.6
0.4
1
0.8
0.6
0.4
0.2
0.2
0
0
-0.2
-0.2
All current must close in the
liquid near the wall – net drag
from jxB force is zero
-0.4
-0.6
-0.8
-1
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•
-0.6
-0.8
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-1
-1
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-0.8
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0
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Net JxB body force p = cVB2
where c = (tw w)/(a )
For high magnetic field and high
speed (self-cooled LM concepts
in inboard region) the pressure
drop is large
The resulting stresses on the
wall exceed the allowable stress
for candidate structural
materials
•
•
Perfect insulators make the net
MHD body force zero
But insulator coating crack
tolerance is very low (~10-7).
–
•
It appears impossible to develop
practical insulators under fusion
environment conditions with large
temperature, stress, and radiation
gradients
Self-healing coatings have been
proposed but none has yet been
found (research is on-going)
Dual Coolant Concept Designs from EU and USA
Cross section of the breeder region unit cell
(ARIES)
Summary
• The D-T Fusion process offers the promise of:
– Virtually unlimited energy source from cheap abundant fuels;
– No atmospheric pollution of greenhouse and acid rain gases;
– Low radioactive burden from waste for future generations.
• Tremendous Progress has been achieved over the past
decades in plasma physics and fusion technology.
• Fusion R&D involves many challenging areas of physics
and technologies and is carried out through extensive
international collaboration
• EU,J, USA, RF, PRC, Korea are about to construct ITER
to demonstrate the scientific and technological feasibility
of fusion energy (ITER will produce 500MW of fusion
power and the project total cost is about $15B)